17.
a + b + c = 0 => [TEX](a + b + c)^2 = 0[/TEX] => [TEX]a^2 + b^2 + c^2 + 2ab + 2bc + 2ac = 0[/TEX]
=> 2ab + 2bc + 2ac = - 2 => ab + bc + ac = -1
=> [TEX](ab + bc + ac)^2 = 1[/TEX]
=> [TEX]a^2b^2 + b^2c^2 + a^2c^2 + 2ab^2c + 2abc^2 + 2a^2bc = 1[/TEX]
<=> [TEX]a^2b^2 + b^2c^2 + a^2c^2 + 2abc(a + b + c) = 1[/TEX]
=> [TEX]a^2b^2 + b^2c^2 + a^2c^2 = 1[/TEX]
[TEX]a^2 + b^2 + c^2 = 2[/TEX] => [TEX](a^2 + b^2 + c^2)^2 = 4[/TEX]
=> [TEX]a^4 + b^4 + c^4 + 2a^2b^2 + 2b^2c^2 + 2a^2c^2 = 4[/TEX]
=> [TEX]a^4 + b^4 + c^4 = 4 - 2(a^2b^2 + b^2c^2 + a^2c^2) = 4 - 2 = 2[/TEX]